(a) Field of the Invention
The present invention relates to a bobbin of which the rotor can be molded without a mold, and a rotor of a wound rotor synchronous motor using the same.
(b) Description of the Related Art
In general, in a WRSM (Wound Rotor Synchronous Motor), a coil is wound around not only a stator, but a rotor as well and current is applied to the coil to create an electromagnetic field. With the increase in cost of raw materials for permanent magnets made of rare earth materials in recent years, efforts for developing a WRSM which can replace an IPMSM (Interior Permanent Magnet Synchronous Motor) have increased.
In particular, a WRSM requires that a coil space factor be increased as high as possible in order to reduce copper loss generated by current flowing the coil wound around the rotor and increase efficiency, and in order to increase the coil space factor, a method of forming not only a stator, but a rotor using core blocks and by inserting a bobbin with a coil wounded in the core blocks is typically used.
A rotor assembled as described above is disposed inside a stator so as to have a predetermined gap, a magnetic field is generated, when power is applied to the coils of the stator and the rotor, and the rotor is rotated by a magnetic action generated between the stator and the rotor. As is well known by those skilled in the art, outer diameter of the rotor are eccentric in nature, e.g., the outer diameters of the core, to reduce any influence from a torque ripple in rotation of the rotor.
On the other hand, in the WRSM that is used for operation of electric motors in electric and hybrid vehicles, the rotor rotates at fairly high speed, e.g., 10000 rpm, during which time the coil wound around the rotor is moved radially outward by the centrifugal force and comes in contact with the core of the stator. In order to correct this phenomenon, a mold has been disposed on an outer surface of the rotor and the coil is fixed on the rotor by injecting a molding material into the spaces between core blocks.
However, the above molding process requires a mold to be aligned in a predetermined line, for rotors which typically have an eccentric outer surface or diameter.
As shown in FIG. 1, a mold is formed in a circle, whereas the outer diameters of core blocks 2 of a rotor eccentrically change so that the outer circumferences curve inward as they come closer to both ends thereof from the centers, such that when a mold is formed to fit along the center line A of the outer diameters of the core blocks 2, both sides 4 and 6 out of the center of the outer diameters of the core blocks rotate and a molding material becomes detached.
Additionally, when a mold is formed to fit along a line B at a predetermined distance from the outer diameters of core blocks in order to prevent this detachment, the gap between the inner diameter of a stator and the outer diameter of the rotator increases, and this resists the flow of a magnetic flux.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.